When a car is operated with the interior thereof warmer than the exterior, the inner surfaces of the window panes become fogged. In some instances when the outside air is very cold, frost accumulates on the outside of the window panes. In order to defrost, the driver turns on the compressor manually, adjusts the ventilation volume of outdoor air by adjusting the blower fan, sets a defrost mode by adjusting a mode setting lever. Such an operation distracts the driver and interferes with driving. In addition to this operation, a rear heater wire printed on the rear window pane is energized in order to defrost and this feature consumes more current.